1. Field of the Invention
The invention relates to a method for regulating the power of a rail motor supplied with power via a direct current catenary. It relates more particularly to a method of regulating the power demanded by the rail motor as a function of the power available to the catenary. The invention also relates to a system for implementing the method.
2. Description of the Prior Art
Direct current power is usually supplied to a rail motor by means of a catenary supplied with power by substations arranged along the railroad track. The substations are rated to supply a particular power and if the power absorbed by a rail motor is greater than the power available to the catenary, either because a plurality of railroad vehicles are on a portion of track supplied with power by the substation at the same time, or because the catenary is not supplied with power correctly because of engineering works or a long distance between substations, voltage drops occur at the power supply substations that can cause a circuit-breaker to trip out in response to an overload or a circuit-breaker in the rail motor to trip out because the voltage is too low.
Solving this problem by placing on board the rail motor a manual selector for limiting the power of the rail motor, which the driver must set to a position defined in the driver""s manual, is known in the art. However, this kind of system is based on nominal operating conditions and does not automatically adapt the power demanded by the rail motor to variations in operating conditions. Accordingly, this kind of system governs the power of the rail motor in a manner that takes account of the worst case scenario operating conditions and cannot benefit from areas supplied with more power, for example near the substations, where the rail motor can consume more power.
Another prior art solution determines the maximum power that the rail motor can consume by measuring the catenary voltage. This solution is generally effective if the rail motor is not too far from the substation. However, if it is at a great distance from the substation, the resistance of the catenary becomes high and the line voltage then depends very considerably on the current flowing in the catenary and thus on the power absorbed by the rail motor. In a situation of this kind, a small increase in consumption implies a large catenary voltage drop and, the action of the power limiting algorithm being a function of the catenary voltage, the gain of the regulation system becomes higher and higher, resulting in an unstable power regulation system.
The object of the present invention is therefore to propose a stable method and system for regulating the power of a rail motor that ensure optimum operation of the rail motor as a function of the power available to the catenary.
The invention provides a method of regulating the power demanded by a rail motor including current collector means cooperating with a catenary supplied with direct current power by power supply substations distributed along the track, which method includes the steps of:
measuring the catenary voltage Vcat at the rail motor;
measuring the catenary current Icat at the rail motor;
evaluating the no-load voltage Vcat0 of the substation supplying power to the catenary to which the rail motor is connected;
evaluating the maximum power available to the catenary from the equation:       P    ⁢          xe2x80x83        ⁢    max    =                    (                  Vcat          0                )            2              4      *      R      
where R is the resistance of the catenary calculated from the equation:       R    =                  (                              Vcat            0                    -          Vcat                )            Icat        ;
and
limiting the power demanded by the rail motor to a power limit Plim less than or equal to the calculated maximum power Pmax.
According to another feature of the invention the no-load voltage Vcat0 of the substation is evaluated by correcting the value of the theoretical no-load voltage Vcat0xe2x80x2 of the substation by means of a proportional-integral regulator whose input is the difference Rxe2x80x2xe2x88x92R, where Rxe2x80x2 is the dynamic resistance of the catenary.
According to another feature of the invention the power limit Plim is calculated by applying to the calculated power Pmax a reducing coefficient K from 0 to 1 taking account of limitations imposed by the infrastructures.
The invention also provides a system for regulating the power demanded by a rail motor including current collector means cooperating with a catenary supplied with direct current power by power supply substations distributed along the track, which system includes:
means for measuring the catenary voltage Vcat at the rail motor;
means for measuring the catenary current Icat at the rail motor;
a stage for evaluating the no-load voltage Vcat0 of the substation supplying power to the catenary to which the rail motor is connected;
a stage for evaluating the maximum power Pmax available to the catenary including a module for calculating the equivalent resistance   R  =            (                        Vcat          0                -        Vcat            )        Icat  
and a module for calculating the power             P      ⁢              xe2x80x83            ⁢      max        =                            (                      Vcat            0                    )                2                    4        *        R              ;
and
means for limiting the power demanded by the rail motor to a value less than or equal to the calculated maximum power Pmax.
Particular embodiments of the power regulation system according to the invention can have one or more of the following features alone or in any technically feasible combination:
the stage for evaluating the substation voltage Vcat0 includes at least one memory delivering a signal Vcat0xe2x80x2 corresponding to the theoretical no-load voltage of the substation supplying power to the rail motor, said signal Vcat0xe2x80x2 serving as a basic value for evaluating the substation voltage Vcat0.
the stage for evaluating the substation voltage Vcat0 further includes means for producing a correction signal that is injected into the theoretical no-load signal Vcat0xe2x80x2 and is produced by a proportional-integral regulator which receives as input the difference Rxe2x80x2xe2x88x92R, where Rxe2x80x2 is the dynamic resistance of the catenary.
the maximum power Pmax is corrected by a multiplier coefficient K obtained from a reducer module taking account of limitations imposed by the infrastructure.
the means for measuring the catenary voltage Vcat and the catenary current Icat are sensors carried by the current collector means.
The subject matter, aspects and advantages of the present invention will be better understood from the following description of one embodiment of the invention, which is described by way of nonlimiting example and with reference to the accompanying drawings.